I have heard great things about Swift but haven't spent a second looking into it because I assumed it's an Apple exclusive language - making it unsuitable for my use case of services deployed on Linux, developed from any OS. To what extent, if any, is Swift exclusive to Apple devices?
You'll have a much better time programming C# on Windows or Swift on macOS, because that's where all the best tooling is. The tools and libraries are open-source, cross-platform, and mostly maintained by one company.